it's now mandatory to be signed into a real account in order to sign up for the In Stock Notification
Not my version!
But, the history of this is me customising it to death long ago for multi-language, attributes (almost) and better admin, before only recently opening a Github with the intention of incorporating these changes and updating it for php8.1 and ZC158. Which has not happened.
So, it appears I am not familiar with the functionality of what is in Github.
But, I would be suprised if it demanded an account for a subscription, that is a customer killer.